Have you ever met someone who was having sex almost nightly for several months ? They are drained, mellowed, tired, sometime sick, and they just dont look or feel right.
Funny story about that actually. About a year ago I was juggling three different girls on a daily basis, having sex 2 or 3 times a day... And I was training harder in the gym than I had since I was 18...

I've never experienced being drained, mellowed, tired or sick from sexual activity.

Though an emotionally draining, nagging girlfriend with whom sex was infrequent, did that to me real quick.